Protandric simultaneous hermaphroditism in the shrimps Lysmata bahia and Lysmata intermedia

Abstract. The sexual system of two peppermint shrimps, Lysmata bahia and Lysmata intermedia, inhabiting intertidal fossil coral terraces at Bocas del Toro, on the Caribbean coast of Panama, was examined. Dissections suggested that the population of each species consisted of functional males and functional simultaneous hermaphrodites. Males have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well‐developed male portion full of sperm, but an undeveloped female portion. Hermaphrodites lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well‐developed ovaries full of mature oocytes and testes with sperm. When hermaphrodites were maintained in pairs, both molted and spawned eggs (to beneath abdomen) that continued developing after 3 d, demonstrating that hermaphrodites can reproduce as males and inseminate other hermaphrodites acting as females. The possibility of self‐fertilization or parthenogenetic reproduction was tested and disregarded, because hermaphrodites reared in isolation spawned oocytes that failed to develop, disappearing from the abdomen after 2 d. Males reared in pairs mature as hermaphrodites in <50 d, showing the ability of males to mature as hermaphrodites. These results demonstrate that L. bahia and L. intermedia are protandric simultaneous hermaphrodites, as reported for all species of this genus whose sexual system has been examined. However, the studied species featured a lifestyle, termed “tropical‐low abundance,” here not recognized previously for the genus; they occur in low abundances in tropical environments, they do not develop symbiotic associations with sessile invertebrates, and they are not conspicuously colored. Information on the sexual systems and lifestyles of more species needs to be examined before these observations can be placed into a comparative context within the genus.     

Gonad Morphology, Colony Demography and Evidence for Hermaphroditism in Gobiodon Okinawae (Teleostei, Gobiidae)

Gobiodon okinawae is a small-sized, obligate coral-dwelling goby. The majority of species in this Indo-Pacific genus exhibit an obligatory association with branching live corals and a number have been shown to be bi-directional hermaphrodites in which adults have the capacity to shift between male and female function. Gonadal histology in G. okinawae demonstrated that all individuals had either an ovotestis or an ovary. Some females had an ovary with vitellogenic oocytes, indicating adult female function. Hermaphrodites having an ovotestis were either functionally male, as evidenced by the presence of spermatozoa or, in one instance, functionally female so judged by the presence of vitellogenic oocytes. No individuals were found to have mature gametes of both sexes, although a number of hermaphrodites had an inactive ovotestis with no mature gametes of either sex. Based on size ranges for fish having different gonad morphologies, individuals in this species appear to develop first as a female. They then either mature and function solely as a female, or become hermaphroditic. Findings based on experimentally maintained individuals suggests that adult hermaphrodites can shift sexual function in either direction. Accessory gonadal structures (AGS) were found in both sexes. These consisted of two fully differentiated pairs of lobes, each compartmentalized internally by lumina and containing PAS+secretions. The secretions of the dorsally located AGS were colloidal while those of the ventrally located AGS were fibrillar and granular in nature. The presence of two sets of AGS among males appears to be characteristic of both Gobiodon and its putative sister genus, Paragobiodon. However, the occurrence of fully developed AGS in both females and males has not previously been reported and may be unique to G. okinawae.     

Plasticity in sex allocation in the plant Mercurialis annua is greater for hermaphrodites sampled from dimorphic than from monomorphic populations

Plants are notoriously variable in gender, ranging in sex allocation from purely male through hermaphrodite to purely female. This variation can have both a genetic and an adaptive plastic component. In gynodioecious species, where females co‐occur with hermaphrodites, hermaphrodites tend to shift their allocation towards greater maleness when growing under low‐resource conditions, either as a result of hermaphrodites shifting away from an expensive female function, or because of enhanced siring advantages in the presence of females. Similarly, in the androdioecious plant Mercurialis annua, where hermaphrodites co‐exist with males, hermaphrodites also tend to enhance their relative male allocation under low‐resource conditions. Here, we ask whether this response differs between hermaphrodites that have been evolving in the presence of males, in a situation analogous to that supposed for gynodioecious populations, vs. those that have been evolving in their absence. We grew hermaphrodites of M. annua from populations in which males were either present or absent under different levels of nutrient availability and compared their reaction norms. We found that, overall, hermaphrodites from populations with males tended to be more female than those from populations lacking males. Importantly, hermaphrodites' investment in pollen and seed production was more plastic when they came from populations with males than without them, reducing their pollen production at low resource availability and increasing their seed production at high resource availability. These results are consistent with the hypothesis that plasticity in sex allocation is enhanced in hermaphrodites that have likely been exposed to variation in mating opportunities due to fluctuations in the frequency of co‐occurring males.     

Co-existence of subadult males and females as alternative tactics of breeding post acquisition in a monogamous and protandrous anemonefish

Summary The monogamous and protandrous anemonefish,Amphiprion clarkii, utilizes only large host sea anemones as breeding sites. Under conditions of breeding site shortage, an important strategy for unmated fish may be to prepare themselves to enter quickly a breeding site from which a breeding male or female has recently disappeared. There are two types of subadults. Some juveniles become subadult males, which can change either to male or female afterwards, but others become subadult females, which can change only to female. Subadult females seem to acquire female posts more easily than subadult males. We develop an ESS model which evaluates the future reproductive success of subadult females and subadult males and test whether coexistence of subadult males and females can be interpreted as adaptive alternative tactics, using field data from two populations. The model predicts that if mortality does not differ between adult males and females the frequency for juveniles to become subadult females should be equal to the proportion of breeding post acquisition by subadult females among that by all subadults. The model also predicts that if mortality does not differ between subadult males and females, nor in adults, the frequency of subadult females among all subadults should be equal to the proportion of post acquisition. The model, with data from two study sites, suggests that alternative life-history pathways found inA. clarkii have evolved through adaptive tactics of breeding post acquisition.     

Environmental stress maintains trioecy in nematode worms

Sex is determined by chromosomes in mammals but it can be influenced by the environment in many worms, crustaceans, and vertebrates. Despite this, there is little understanding of the relationship between ecology and the evolution of sexual systems. The nematode Auanema freiburgensis has a unique sex determination system in which individuals carrying one X chromosome develop into males while XX individuals develop into females in stress-free environments and self-fertile hermaphrodites in stressful environments. Theory predicts that trioecious populations with coexisting males, females, and hermaphrodites should be unstable intermediates in evolutionary transitions between mating systems. In this article, we study a mathematical model of reproductive evolution based on the unique life history and sex determination of A. freiburgensis. We develop the model in two scenarios, one where the relative production of hermaphrodites and females is entirely dependent on the environment and one based on empirical measurements of a population that displays incomplete, “leaky” environmental dependence. In the first scenario environmental conditions can push the population along an evolutionary continuum and result in the stable maintenance of multiple reproductive systems. The second “leaky” scenario results in the maintenance of three sexes for all environmental conditions. Theoretical investigations of reproductive system transitions have focused on the evolutionary costs and benefits of sex. Here, we show that the flexible sex determination system of A. freiburgensis may contribute to population-level resilience in the microscopic nematode's patchy, ephemeral natural habitat. Our results demonstrate that life history, ecology, and environment may play defining roles in the evolution of sexual systems.     

Maternal effects on offspring growth and development depend on environmental quality in the frogBombina orientalis

Summary Differences in maternal investment and initial offspring size can have important consequences for offspring growth and development. To examine the effects of initial size variability in the frogBombina orientalis, we reared larvae (N=360) in one of two treatments representing different levels of environmental quality. We used snout-vent length at the feeding stage (stage 25, Gosner 1960) as a measure of maternal investment. In a “low quality” treatment, larvae were reared with two conspecific tadpoles and food was limited, whereas in a “high quality” treatment, larvae were reared individually and were fed ad libitum. Among tadpoles reared in the low quality treatment, individuals that were initially small had smaller body sizes through metamorphosis and longer larval periods than individuals that were initially large. Among tadpoles reared in the high quality treatment, initial size had only a weak influence on later larval size, and did not significantly affect metamorphic size of the duration of the larval period. This interaction between maternal investment and rearing conditions suggests that production of initially small offspring could be advantageous if these offspring develop in relatively benign environments, but disadvantageous if environments are more severe. These findings are discussed in light of previous studies that have demonstrated such interactions in organisms with complex life cycles.     

XY female mice express H-Y antigen

Karyotypically XY individuals of the C57BL/6J-Y^POS mouse stock develop as females or hermaphrodites, but never as normal males. The aberrant sexual development results from the interaction of the C57BL/6J genetic background with the M. poschiavinus-derived Y chromosome. XY females from this stock were assayed for H-Y antigen. By the criteria of skin-grafting, the cell-mediated lympholysis test, and the popliteal lymph node assay, these XY females are antigenically indistinguishable from normal C57BL/6 males. Implications for the hypothesis that H-Y antigen induces formation of the mammalian testis are discussed.     

On the possible role of nonreproductive traits for the evolution of unisexuality: Life‐history variation among males,females, and hermaphrodites in Opuntia robusta (Cactaceae)

In angiosperms, dioecy has arisen in 871–5,000 independent events, distributed in approximately 43% of the flowering families. The reproductive superiority of unisexuals has been the favorite explanation for the evolution of separate sexes. However, in several instances, the observed reproductive performance of unisexuals, if any, does not seem to compensate for the loss of one of the sex functions. The involvement of fitness components not directly associated with reproduction is a plausible hypothesis that has received little attention. Life‐history traits recently recognized as predictors of plant performance were compared among males, females, and hermaphrodites of a rare trioecious Opuntia robusta population in the field, using the cladode as the study unit. Cladode mortality by domestic herbivores was common and higher in females and hermaphrodites than in males. Males, females, or both displayed lower shrinkage and higher rates of survival, growth, and reproductive frequency than hermaphrodites. Unisexuals simultaneously outperformed hermaphrodites in demographic traits known to compete for common limiting resources, such as the acceleration of reproductive maturation (progenesis) and survival. A meta‐analysis combining the outcomes of each of the analyzed life‐history traits revealed a tendency of males (d₊₊ = 1.03) and females (d₊₊ = 0.93) to outperform hermaphrodites in presumably costly demographic options. Clonality is induced by human or domestic animal plant sectioning; and males and females highly exceeded hermaphrodites in their clonality potential by a factor of 8.3 and 5.3, respectively. The performances of unisexuals in the analyzed life‐history traits may enhance their reproductive potential in the long run and their clonality potential and could explain the observed increase of unisexuality in the population. Life‐history traits can be crucial for the evolution of unisexuality, but their impact appears to be habitat specific and may involve broad ontogenetic changes.     

Ecological disjunction across the sexes in an alloparasitoid: Host requirements,sex ratios and mate localization (Hymenoptera: Aphelinidae)

The larval females of Coccophagus sp. nr gurneyi Compere are primary parasitoids of lantana mealybugs, whereas males develop hyperparasitically through other parasitoids (never their own females), so the species is alloparasitic. Males are seldom even reared from lantana mealybugs (<0.3%, n = 4,212), and have not yet been reared from any other host. Adults were sampled in the field to establish that this species is sexual (by assessing female spermathecal content), and to quantify relative abundance of the sexes around host infestations. Adult males were scarce above hosts (3%, n = 314), but were attracted in relatively high numbers to caged virgin females within those infestations. Caged females outside infestations did not attract males, suggesting that mate attraction requires environmental signals other than those from females. Most females collected in the field above host infestations had sperm in their spermathecal capsules. They presumably had mated with males that developed elsewhere (so mate localization might involve searching across substantial distances). Virgin females were present only early in the day and evidently mate soon after eclosion. Evidence of sperm depletion in mated females was not found. The spatial scale of male and female movements needs to be quantified, but the ongoing movement of individuals (as a consequence of their sex‐related host relationships) seems to be a regular aspect of their ecology. The spatial and temporal dynamics across the sexes illustrates that their abilities to localize one another for mating leaves the sexes free to diverge ecologically, and their sex ratios to vary.     

Sex Determination in Freshwater Eels and Management Options for Manipulation of Sex

Catadromous eels enter fresh water as sexually undifferentiated glass eels and develop into males and females before migrating back to sea as silver eels. Females develop ovaries directly from the ambiguous primordial gonad whereas males pass through a transitional intersexual stage before developing testes. Eels have sex-specific life-history strategies. Males may grow faster than females initially, but this difference is soon reversed and females attain a greater age- and size-at-metamorphosis than males. Male fitness is maximized by maturing at the smallest size that allows a successful spawning migration (a time-minimizing strategy) whereas females adopt a more flexible size-maximizing strategy that trades off pre-reproductive mortality against fecundity. Although heteromorphic sex chromosomes have been identified in some species, the sex of developing gonads is labile and gender is determined principally by environmental factors. Individuals experiencing rapid growth prior to gonad differentiation tend to develop as males, whereas eels that grow slowly initially are more likely to develop as females. Paradoxically, males tend to predominate under conditions of high density, which may be because a male “grow quickly, mature early” strategy increases an individual’s chances of survival during periods of intraspecific competition. High temperatures and saline conditions have also been proposed to favor development as males but experimental studies have failed to demonstrate a clear effect of either on sex determination. High proportions of female silver eels migrating from some upstream areas, lakes and large rivers may be due to low population density or poor conditions for growth in these habitats. Manipulating sex ratios in favor of females has the potential to increase eel production in aquaculture and to buffer natural populations against fishing pressure. Sex steroids (oestrogens and phytoestrogens) have a strong feminizing effect on undifferentiated individuals and are most effective when targeted at younger eels and administered at high doses for prolonged periods. Modifying local environmental conditions, in particular reducing eel density and limiting interference and social stress, may also promote the development of females. Further research into the timing and mechanisms of sex determination in eels is required to effectively and efficiently manipulate sex for conservation and/or economic benefit.     

Sex determination in the androdioecious barnacle Scalpellum scalpellum (Crustacea: Cirripedia)

How androdioecy (coexistence of hermaphrodites and males) is maintained is still poorly understood. Therefore, sex determination was studied in the androdioecious barnacle Scalpellum scalpellum L. First, 247 cypris larvae from seven broods were investigated for sexual dimorphism in larval morphology and found to be all identical. Second, experiments with cyprids showed that males and hermaphrodites differ distinctly in morphology as soon as 4–5 days after settlement. Third, 14 252 cyprids were allowed to settle on the bottom of their culture cages, and all surviving larvae developed into hermaphrodites and none into dwarf males. Fourth, larvae settled in hermaphrodite receptacles (i.e. future males) were removed at increasing intervals after settlement to study if the male and hermaphrodite sexual expressions are fixed or plastic. All larvae became dwarf males if allowed to stay there for more than 8 h after settlement. But if removed within 3 h after settlement, half of them developed into hermaphrodites. We conclude that an environmental sex determination mechanism operates in S. scalpellum. Together with a 1:1 hermaphrodite/male ratio observed in previously reported experiments offering a free choice of settlement, we suggest that all larvae are potential hermaphrodites, but only 50% can settle in hermaphrodite receptacles and yield males.     

Sex allocation in a simultaneous hermaphrodite, the blue-banded goby (Lythrypnus dalli): the effects of body size and behavioral gender and the consequences for reproduction

Although species with both male and female sexual functionsare often dichotomized into simultaneous and sequential hermaphrodites,many simultaneous hermaphrodites also exhibit sequential changesin sex allocation. In a field experiment using one such species,the gobiid fish, Lythrypnus dalli, female-biased individualsreallocated to male function in relation to their relative bodysize: consistent with the sizeadvantage hypothesis, large femaleswere more likely to reallocate and large fish had the highestspawningrates. Individuals, despite internal allocation to bothsexual functions, adopted only one behavioral gender. Behavioralmales had higher reproductive rates than behavioral females,and laboratory experiments showed that females preferred tomate with large males. Behavioral males grew more rapidly anddid notdiffer from behavioral females in survivorship. In addition,individuals who adopted male behavior but did not receive eggsin their nests maintained high levels of female tissue, whereasmales that received eggs did not. Laboratory experiments showedthat, unlike most hermaphroditic animals, L. dalli canchangeallocation either from ‘female’ to ‘male’or from ‘male’ to ‘female’. Thus, L.dalli shares haracteristics of both sequential and simultaneoushermaphrodites. Simultaneous hermaphroditism maybe maintained,in this species, to facilitate rapid sex change from femaleto male and to retain flexibility o that unsuccessful malescan revert to reproduction as females.     

Implications for the Maintenance of Androdioecy in the Freshwater Shrimp, Eulimnadia texana Packard: Encounters between Males and Hermaphrodites are not Random

Androdioecy is a mixed‐mating system in which there are males and hermaphrodites but no pure females. Few species exhibit such a mating system. Eulimnadia texana is a branchiopod crustacean that has recently been identified as an androdioecious species. This system is ideal for testing questions related to the evolution of sexual reproduction. We are testing a model that predicts androdioecy to be a stable mixed‐mating system under certain conditions. Specifically, we investigated whether encounters between males and hermaphrodites are random or if either sex seeks out the other for mating. Focal male or hermaphrodite clam shrimp were presented with stimulus shrimp of the other sex or kept alone. Swimming speed and time spent within different areas of a test chamber were recorded. Males did not alter mean swimming speed or spend more time than expected by chance near partitioned hermaphrodites. Hermaphrodites, however, decreased mean swimming speed in the presence of males and also spent more time than expected by chance near partitioned males, suggesting that hermaphrodites respond to male chemical and/or visual stimuli. Modified swimming behaviour probably facilitates inter‐sexual contact, thereby increasing opportunities for out‐crossing above that expected by random encounters.     

Selfish male‐determining element favors the transition from hermaphroditism to androdioecy

According to the current, widely accepted paradigm, the evolutionary transition from hermaphroditism toward separate sexes occurs in two successive steps: an initial, intermediate step in which unisexual individuals, male or female, sterility mutants coexist with hermaphrodites and a final step that definitively establishes dioecy. Two nonexclusive processes can drive this transition: inbreeding avoidance and reallocation of resources from one sexual function to the other. Here, we report results of controlled crosses between males and hermaphrodites in Phillyrea angustifolia, an androdioecious species with two mutually intercompatible, but intraincompatible groups of hermaphrodites. We observed different segregation patterns that can be explained by: (1) epistatic interactions between two unlinked diallelic loci, determining sex and mating compatibility, and (2) a mutation with pleiotropic effects: female sterility, full compatibility of males with both hermaphrodite incompatibility groups, and complete male‐biased sex‐ratio distortion in one of the two groups. Modeling shows that these mechanisms can explain the high frequency of males in populations of P. angustifolia and can promote the maintenance of androdioecy without requiring inbreeding depression or resource reallocation. We thus argue that segregation distortion establishes the right conditions for the evolution of cryptic dioecy and potentially initiates the evolution toward separate sexes.     

Sexual dimorphism in gender plasticity and its consequences for breeding system evolution

Flowering plants are able to develop gametes throughout their lives. As a consequence, environmental conditions can impact this development and alter a plant's functional gender or the degree to which it achieves fitness through male or female function. Two dimorphic breeding systems are widespread among angiosperm families: gynodioecy (hermaphrodites and females) and dioecy (males and females). Gynodioecy can evolve into dioecy, via loss of female function on the hermaphrodites, or it can remain stable. Here I discuss how developmental plasticity of gender can impact the sex ratio of populations and thereby influence the transition of one breeding system into another. I review studies showing that greater plasticity of fruit production by hermaphrodites as compared with females causes sex ratios among populations to vary in response to environmental conditions, with higher female frequency expected in harsh or low-quality sites. I also review how dioecy may evolve in dry sites to avoid inbreeding and any consequent inbreeding depression. Taken together, these studies show the importance of understanding how ecological development affects functional gender and consequently the evolutionary stability or malleability of dimorphic breeding systems.     

Density‐dependent sex‐biased development of macroptery in a water strider

In wing‐polymorphic insects, wing morphs differ not only in dispersal capability but also in life history traits because of trade‐offs between flight capability and reproduction. When the fitness benefits and costs of producing wings differ between males and females, sex‐specific trade‐offs can result in sex differences in the frequency of long‐winged individuals. Furthermore, the social environment during development affects sex differences in wing development, but few empirical tests of this phenomenon have been performed to date. Here, I used the wing‐dimorphic water strider Tenagogerris euphrosyne to test how rearing density and sex ratio affect the sex‐specific development of long‐winged dispersing morphs (i.e., sex‐specific macroptery). I also used a full‐sib, split‐family breeding design to assess genetic effects on density‐dependent, sex‐specific macroptery. I reared water strider nymphs at either high or low densities and measured their wing development. I found that long‐winged morphs developed more frequently in males than in females when individuals were reared in a high‐density environment. However, the frequency of long‐winged morphs was not biased according to sex when individuals were reared in a low‐density environment. In addition, full‐sib males and females showed similar macroptery incidence rates at low nymphal density, whereas the macroptery incidence rates differed between full‐sib males and females at high nymphal density. Thus complex gene‐by‐environment‐by‐sex interactions may explain the density‐specific levels of sex bias in macroptery, although this interpretation should be treated with some caution. Overall, my study provides empirical evidence for density‐specific, sex‐biased wing development. My findings suggest that social factors as well as abiotic factors can be important in determining sex‐biased wing development in insects.     

A Single Genetic Determinant that Prevents Sex Reversal in C57BL-YPOS Congenic Mice

Sex determination in the mammalian embryo begins with the activation of a gene on the Y chromosome which triggers a cascade of events that lead to male development. The mechanism by which this gene, designated SRY in humans and Sry in mice (sex determining region of the Y chromosome), is activated remains unknown. Likewise, the downstream target genes for Sry remain unidentified at present. C57BL mice carrying a Y chromosome from Mus musculus musculus or molossinus develop normally as males. In contrast, C57BL/6 mice with the Y chromosome from M. m. domesticus often show sex reversal, i.e., develop as XY females. It has been documented that C57BL mice with the Y chromosome from Poschiavinus (Y^POS), a domesticus subtype, always develop as females or hermaphrodites. This suggests that a C57BL gene either up- or downstream of Sry is ineffective in interacting with Sry, which then compromises the processes that lead to normal male sex development. Nonetheless, by selective breeding, we have been able to generate a sex reversal-resistant C57BL/6-congenic strain of mice in which the XY^POS individuals consistently develop as normal males with bilateral testes. Because the resistance to sex reversal was transferred from strain 129S1/Sv (nonalbino) by simple selection over 13 backcross generations, it is inferred that a single autosomal gene or chromosomal region confers resistance to the sex reversal that would otherwise result. XY^POS normal males generated in these crosses were compared to XY^POS abnormal individuals and to C57BL/6 controls for sexual phenotype, gonadal weight, serum testosterone, and major urinary protein (MUP) level. A clear correlation was found among phenotypic sex, MUP level, and testis weight in the males and in the incompletely masculinized XY^POS mice. The fully masculinized males of the congenic strain resemble C57BL/6 males in the tested parameters. DNA analysis confirmed that these males, in fact, carry the Y^POS Sry gene.     

Phenotypic plasticity of hermaphrodite sex allocation promotes the evolution of separate sexes: an experimental test of the sex-differential plasticity hypothesis using Sagittaria latifolia (Alismataceae)

Separate sexes can evolve under nuclear inheritance when unisexuals have more than twice the reproductive fitness of hermaphrodites through one sex function (e.g., when females have more than twice the seed fertility of hermaphrodites). Because separate sexes are thought to evolve most commonly via a gynodioecious intermediate (i.e., populations in which females and hermaphrodites cooccur), the conditions under which females can become established in populations of hermaphrodites are of considerable interest. It has been proposed that resource-poor conditions could promote the establishment of females if hermaphrodites are plastic in their sex allocation and allocate fewer resources to seed production under these conditions. If this occurs, the seed fertility of females could exceed the doubling required for the evolution of unisexuality under low-, but not high-resource conditions (the sex-differential plasticity hypothesis). We tested this hypothesis using replicate experimental arrays of the aquatic herb Sagittaria latifolia grown under two fertilizer treatments. The results supported the sex-differential plasticity hypothesis, with females having more than twice the seed fertility of hermaphrodites under low-, but not high-fertilizer conditions. Our findings are consistent with the idea that separate sexes are more likely to evolve under unfavorable conditions.     

Altered mating behaviour in a Cry1Ac-resistant strain of Helicoverpa armigera (Lepidoptera: Noctuidae)

Randomness of mating between susceptible and resistant individuals is a major factor that closely relates to the refuge strategy of resistance management for Helicoverpa armigera (Hübner) to Bacillus thuringiensis cotton. The mating behaviour of Cry1Ac‐susceptible and Cry1Ac‐resistant strains of H. armigera was compared to investigate the randomness of their mating. The percentage of mating was lower for Cry1Ac‐resistant H. armigera compared with that of the susceptible strain under both no‐choice and multiple‐choice conditions. The low percentage of mating in the resistant strain indicates a reduced incidence of successful mating. The percentage of spermatophore‐containing mated female H. armigera in the crossing of susceptible females × resistant males was significantly lower than in the crossing of resistant females × susceptible males, but the observed mating frequencies of these two types of cross were similar to each other. This indicates that resistant males reduce the incidence of mating paternity more than they do their mating frequency. The percentages of heterogametic matings (susceptible females × resistant males, resistant females × susceptible males) in the multiple‐choice experiment were lower than those of homogametic matings (susceptible × susceptible, resistant × resistant) on peak mating nights. However, the difference between heterogametic and homogametic mating was not significant, indicating that there was a random mating between susceptible and resistant strains. The results presented here do not reflect reality in mating associated with Cry1Ac resistance but can provide insight into variable expression.     

The effect of cryptic female choice on sex allocation in simultaneous hermaphrodites

Sex allocation theory for simultaneous hermaphrodites has focused primarily on the effects of sperm competition, but the role of mate choice has so far been neglected. We present a model to study the coevolution of cryptic female choice and sex allocation in simultaneous hermaphrodites. We show that the mechanism of cryptic female choice has a strong effect on the evolutionary outcome: if individuals remove a fixed proportion of less-preferred sperm, the optimal sex allocation is more female biased (i.e. more biased towards egg production) than without cryptic female choice; conversely, if a fixed amount of sperm is removed, sex allocation is less female-biased than without cryptic female choice, and can easily become male biased (i.e. biased towards sperm production). Under male-biased sex allocation, hermaphroditism can become unstable and the population can split into pure males and hermaphrodites with a female-biased allocation. We discuss the idea that the evolution of sex allocation may depend on the outcome of sexual conflict over the fate of received sperm: the sperm donor may attempt to manipulate or by-pass cryptic female choice and the sperm recipient is expected to resist such manipulation. We conclude that cryptic female choice can have a strong influence on sex allocation in simultaneous hermaphrodites and strongly encourage empirical work on this question.